Method and apparatus for the radio frequency sputtering of dielectric materials



3,525,680 METHOD AND APPARATUS FOR THE RADIO FREQUENCY SPUTTERING Aug.25, 1970 P. D. DAVIDSE ET AL OF DIELECTRIC MATERIALS Filed Dec. 20, 1965VACUUM PUMP IN VENTORS PIETER D. DAVIDSE WALTER J. KLEINFELDER MA, M4 BYW' W ATTORNEYS FIG.2

United States Patent Ofice METHOD AND APPARATUS FOR THE RADIO FREQUENCYSPUTTERING F DIELECTRIC MATERIALS Pieter D. Davidse, Poughkeepsie, N.Y.,and Walter J. Kleinfelder, Palo Alto, Calif., assignors to InternationalBusiness Machines Corporation, Armonk, N.Y., a corporation of New YorkFiled Dec. 20, 1965, Ser. No. 514,853 Int. Cl. C23c /00 U.S. Cl. 2041924 Claims ABSTRACT OF THE DISCLOSURE An improvement in a system andmethod for radio frequency sputtering of a dielectric material todeposit a film on a substrate whereby a radio frequency power source iscoupled with an electrode associated with a source of dielectricmaterial in an ionization chamber, an ionizable gas is introduced intosaid chamber, a glow discharge is produced and dielectric material issputtered and deposited onto a substrate, said improvement comprisingpassing the current from the output of the radio frequency power sourcethrough a capacitor and thence to the electrode associated with thesource of dielectric material.

The present invention relates to an improved method for sputteringdielectric materials. In particular, the invention relates to animprovement in the radio frequency sputtering of dielectric materials insuch a way that smooth, defect-free films of the dielectric aredeposited onto a substrate.

The sputtering of dielectrics by radio frequency fields is generallydisclosed in an article by G. S. Anderson, William N. Mayer and G. K.Werner appearing in The Journal of Applied Physics, vol. 33, No. 10,October 1962. Another method for sputtering dielectrics is disclosed inapplication Ser. No. 428,733, filed Jan. 28, 1965, now US. Pat.3,369,991.

However, a number of disadvantages attend the use of prior art systemsfor sputtering dielectrics. First, loading of the radio frequency powersupply is difllcult. It is also difficult to bring the standing waveratio down to a low value and small sparks are observed on the groundedsurfaces of the vacuum system. More importantly though is the fact thatthe resulting films deposited by prior techniques are generally roughand defective in that they contain pinholes. Such deficiences make priorprocesses unsatisfactory for use in the deposition of insulating films,such as, glass insulating films used in the production of semiconductordevices.

Therefore, a primary object of the present invention is to provide animproved method for radio frequency sputtering of insulating materials,such as glasses, which overcomes the disadvantages of prior techniquesand results in the deposition of smooth, defect-free, high qualityinsulating films.

The present invention will be more fully appreciated in the light of thefollowing detailed description of a preferred method for practicing theinvention and by reference to the accompanying drawing illustrating apreferred system for carrying out the invention.

In the drawing:

FIG. 1 is a vertical, partly sectional, somewhat schematic view of asputtering system embodying the invention, and

FIG. 2 is a diagram of an electric circuit useful in the sputteringsystem of the invention.

In general, the invention is based upon the discovery that smooth, highquality insulating films can be deposited 3,525,686 Patented Aug. 25,1970 by radio frequency sputtering of dielectric materials byincorporating in the system a capacitor connected in series between theelectrode associated with the source of insulating material and theoutput terminal of a radio frequency generator.

Referring now to FIG. 1 which shows an. exemplary form of sputteringapparatus incorporating the principles of the present invention, a gasionization chamber is enclosed by an envelope 10 in the form of a belljar made of suitable material, such as Pyrex glass, which is removablymounted on a base plate 12. A gasket 11 is disposed between the jar 10and plate 12 to provide a vacuum seal. A suitable gas, such as argon,supplied by a source 13, is maintained at a desired pressure in theenclosure by means of a vacuum pump 14. Within the gas-filled enclosureare positioned an electrode structure, generally designated 16, and asubstrate support structure, generally designated 18.

Considering now the construction of the electrode assembly which isgenerally designated 16, a target 21, consisting of the dielectricmaterial which is to be sputtered, is mounted on or positioned adjacentto a metal electrode 22. This electrode 22 is insulated from a hollowsupporting column or post 24, the bottom flanged portion of which issecured to the base plate 12. The post 24 is electrically conductive,and being in direct electrical contact with the base plate 12 (which isgrounded as indicated in the drawings), the post 24 is maintained atground potential. Supported on the upper flanged end of the cylindricalpost 24 is a metallic shield 26 that partially encloses the electrode 22adjoining the target 21 and protects the electrode from unwantedsputtering.

Insulating bushing 25, insulates shield 26 and post 24 from electrode22. Conductor 27 passes through base 12 and is electrically connectedwith electrode 22. The electrode assembly may also be provided withcooling means, not shown, to control the temperature during operation.The above noted application may be consulted for a more detaileddisclosure of vacuum sputtering apparatus useful in the presentinvention.

Substrate support assembly 18 comprises a support plate 29 on whichsubstrate 30 is mounted by any suitable means. Plate 29 is secured tothe underside of plate 31 which is supported by posts 32, through whichplate 29 is electrically connected to grounded base plate 12.

If the substrate to be coated is of a nature such that it would bedamaged by excessive heat, means can be provided for cooling it duringsputtering. For example, cooling coil 35 is positioned in heat exchangerelationship with metal plate 31. A cooling fluid is circulated throughcoil 35 by input and return conduits, 36 and 37, respectively.

In a particular embodiment, it has also been found desirable to subjectthe glow discharge to a magnetic field. This may be done by stacking aset of toroidal permanent magnets above plate 31 to provide a steadymagnetic field along the vertical axis (arrow 92) of the toroids, normalto the surface of target 21. The direction of the magnetic field, up ordown, is immaterial.

Electrode 22 and conductor 27 are electrically connected by conductor 50with the output of a radio frequency power source 20. Connected inseries between the electrode 22 and the radio frequency power source 20is a capacitor 60. Incorporation'of capacitor 60 in the sputteringsystem, as shown and described, is the primary feature of the invention.By passing the radio frequency output energy through capacitor 60 andthence to electrode 22, it has been found that superior dielectric filmsmay be sputtered from a dielectric source 21, as illustrated. While theexact value of the capacitor used is not critical and will be dependenton the particular systern, capacitors having values of from 100 to20,000 pf. have been used successfully.

Any conventional RF power source 20 may be employed in the describedsputtering system. For example, as illustrated in FIG. 2, the powersource 20 may comprise a conventional RF power supply 80 and matchingcircuit 81. The output of power source 20 is connected electrically withcapacitor 60 and thence with electrode 22.

In operation, the ionization chamber formed by jar 10 and base 12 isevacuated 'by vacuum pump 14 and an ionizable gas such as argon, is bledin through line 13 to maintain the desired pressure in the chamber. Asource of dielectric material and a substrate are positioned in thechamber substantially as shown in FIG. 1. An RF power source is thenactuated and the output is passed through capacitor 60 to the electrode22 associated with the source of dielectric material. The exactconditions of pressure, temperature, power input, etc. are not critical,and may be varied to give the optimum in film thickness and quality forthe specific system employed.

Where a magnetic field is employed, fields having a strength of about100 gauss are eiTective.

As an example of sputtering in accordance with the invention to producesmooth, defect-free films using the system illustrated in FIGS. 1 and 2,fused quartz has been sputtered under the following conditions:

Pressure5 10- torr Atmosphere-100% argon RF power input-7l0 wattsCurrent frequencyl3.56 mc. Substrate-to-target spacing-1 inch Diameterof electrode5" Time 30 minutes Film thickness-55,000 A.

Without capacitor With capacitor Electrode potential 2300 v. pk.-pk.5300 v. pk.-pk.

Forward power 470 watts. 5 watts.

Reflected power 205 watts 5 watts Net input power to cathod 265 watt 290watts Standing Wave ratio 5.5 1.2.

Sputtering time 40 min 120 min.

Film thickness 8,800 A 30,000 A.

Rate of deposition 220 A. [min 250 A. /min.

Quality of film BadRough and ExcellentSmooth full of defects. anddefect-free.

The results of the above comparison show that while sputteringdielectrics at substantially the same rates of film deposition, superiorfilms are deposited by the system in which the capacitor isincorporated. Also, sputtering without the capacitor is relativelyinefiicient in that a much higher power input is required to achieve thesame net input to the electrode associated with 4 the target. Further,with the capacitor, a much lower standing wave ratio is achieved.

It will be apparent to those skilled in the art that superior films ofany suitable dielectric may be deposited in accordance with theinvention, including, for example, fused quartz, borosilicate glasses,calciumaluminosilicate glasses, refractory metal oxides, such asalumina, minerals, such as mullite, etc.

Variations may also be made in the specific arrangement of thesputtering apparatus and circuitry, without departing from the spiritand scope of the invention as expressed in the following claims.

What is claimed is:

1. In a system of apparatus for the radio frequency sputtering of adielectric material to deposit a film onto a substrate, the apparatusconsisting essentially of a lowpressure ionization chamber adapted tocontain the dielectric material and the substrate, a source of gas, asource of radio frequency power for producing a glow discharge in saidgas in said chamber and a diode system consisting essentially of a radiofrequency electrode associated with said dielectric material andelectrically connected with the output of said source of radio frequencypower, and a second electrode the improvement consisting essentially ofa capacitor electrically connected in series between said radiofrequency electrode and the output of said source of radio frequencypower, and positioned outside said ionization chamber, said capacitorhaving a value of from to 20,000 pf.

2. The apparatus of claim 1 further including means for subjecting saidglow discharge to a magnetic field during sputtering.

3. In a method for sputtering a dielectric material by radio frequencystimulated glow discharge, whereby power from a radio frequency powersource is coupled with an electrode associated with a source ofdielectric material in an ionization chamber, an ionizable gas isintroduced into said chamber, a glow discharge is produced anddielectric material is sputtered and deposited onto a substrate,

the improvement c0nsisting essentially of stimulating said glowdischarge by passing the current from the output of said radio frequencypower source through a capacitor positioned outside said ionizationchamber and thence to a diode system consisting essentially of anelectrode associated with said source of dielectric material, saidcapacitor having a value of from 100 to 20,000 pf. and a secondelectrode.

4. The method of claim 3 further consisting essentially of subjectingsaid glow discharge to a magnetic field during sputtering.

References Cited UNITED STATES PATENTS 3,233,137 2/1966 Anderson et a1204192 3,021,271 2/1962 Wehner 204-l92 3,347,772 10/1967 Laegreid et a1.204298 ROBERT K. MIHALEK, Primary Examiner US. Cl. X.R. 204298

